text: /*
   * NTP state machine interfaces and logic.
   *
   * This code was mainly moved from kernel/timer.c and kernel/time.c
   * Please see those files for relevant copyright info and historical
   * changelogs.
   */
  #include <linux/capability.h>
  #include <linux/clocksource.h>
  #include <linux/workqueue.h>
  #include <linux/hrtimer.h>
  #include <linux/jiffies.h>
  #include <linux/math64.h>
  #include <linux/timex.h>
  #include <linux/time.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  
  #include "tick-internal.h"
  
  /*
   * NTP timekeeping variables:
   */
  
  DEFINE_SPINLOCK(ntp_lock);
  
  
  /* USER_HZ period (usecs): */
  unsigned long			tick_usec = TICK_USEC;
  
  /* ACTHZ period (nsecs): */
  unsigned long			tick_nsec;
  
  static u64			tick_length;
  static u64			tick_length_base;
  
  #define MAX_TICKADJ		500LL		/* usecs */
  #define MAX_TICKADJ_SCALED \
  	(((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
  
  /*
   * phase-lock loop variables
   */
  
  /*
   * clock synchronization status
   *
   * (TIME_ERROR prevents overwriting the CMOS clock)
   */
  static int			time_state = TIME_OK;
  
  /* clock status bits:							*/
  static int			time_status = STA_UNSYNC;
  
  /* TAI offset (secs):							*/
  static long			time_tai;
  
  /* time adjustment (nsecs):						*/
  static s64			time_offset;
  
  /* pll time constant:							*/
  static long			time_constant = 2;
  
  /* maximum error (usecs):						*/
  static long			time_maxerror = NTP_PHASE_LIMIT;
  
  /* estimated error (usecs):						*/
  static long			time_esterror = NTP_PHASE_LIMIT;
  
  /* frequency offset (scaled nsecs/secs):				*/
  static s64			time_freq;
  
  /* time at last adjustment (secs):					*/
  static long			time_reftime;
  
  static long			time_adjust;
  
  /* constant (boot-param configurable) NTP tick adjustment (upscaled)	*/
  static s64			ntp_tick_adj;
  
  #ifdef CONFIG_NTP_PPS
  
  /*
   * The following variables are used when a pulse-per-second (PPS) signal
   * is available. They establish the engineering parameters of the clock
   * discipline loop when controlled by the PPS signal.
   */
  #define PPS_VALID	10	/* PPS signal watchdog max (s) */
  #define PPS_POPCORN	4	/* popcorn spike threshold (shift) */
  #define PPS_INTMIN	2	/* min freq interval (s) (shift) */
  #define PPS_INTMAX	8	/* max freq interval (s) (shift) */
  #define PPS_INTCOUNT	4	/* number of consecutive good intervals to
  				   increase pps_shift or consecutive bad
  				   intervals to decrease it */
  #define PPS_MAXWANDER	100000	/* max PPS freq wander (ns/s) */
  
  static int pps_valid;		/* signal watchdog counter */
  static long pps_tf[3];		/* phase median filter */
  static long pps_jitter;		/* current jitter (ns) */
  static struct timespec pps_fbase; /* beginning of the last freq interval */
  static int pps_shift;		/* current interval duration (s) (shift) */
  static int pps_intcnt;		/* interval counter */
  static s64 pps_freq;		/* frequency offset (scaled ns/s) */
  static long pps_stabil;		/* current stability (scaled ns/s) */
  
  /*
   * PPS signal quality monitors
   */
  static long pps_calcnt;		/* calibration intervals */
  static long pps_jitcnt;		/* jitter limit exceeded */
  static long pps_stbcnt;		/* stability limit exceeded */
  static long pps_errcnt;		/* calibration errors */
  
  
  /* PPS kernel consumer compensates the whole phase error immediately.
   * Otherwise, reduce the offset by a fixed factor times the time constant.
   */
  static inline s64 ntp_offset_chunk(s64 offset)
  {
  	if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
  		return offset;
  	else
  		return shift_right(offset, SHIFT_PLL + time_constant);
  }
  
  static inline void pps_reset_freq_interval(void)
  {
  	/* the PPS calibration interval may end
  	   surprisingly early */
  	pps_shift = PPS_INTMIN;
  	pps_intcnt = 0;
  }
  
  /**
   * pps_clear - Clears the PPS state variables
   *
   * Must be called while holding a write on the ntp_lock
   */
  static inline void pps_clear(void)
  {
  	pps_reset_freq_interval();
  	pps_tf[0] = 0;
  	pps_tf[1] = 0;
  	pps_tf[2] = 0;
  	pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
  	pps_freq = 0;
  }
  
  /* Decrease pps_valid to indicate that another second has passed since
   * the last PPS signal. When it reaches 0, indicate that PPS signal is
   * missing.
   *
   * Must be called while holding a write on the ntp_lock
   */
  static inline void pps_dec_valid(void)
  {
  	if (pps_valid > 0)
  		pps_valid--;
  	else {
  		time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
  				 STA_PPSWANDER | STA_PPSERROR);
  		pps_clear();
  	}
  }
  
  static inline void pps_set_freq(s64 freq)
  {
  	pps_freq = freq;
  }
  
  static inline int is_error_status(int status)
  {
  	return (time_status & (STA_UNSYNC|STA_CLOCKERR))
  		/* PPS signal lost when either PPS time or
  		 * PPS frequency synchronization requested
  		 */
  		|| ((time_status & (STA_PPSFREQ|STA_PPSTIME))
  			&& !(time_status & STA_PPSSIGNAL))
  		/* PPS jitter exceeded when
  		 * PPS time synchronization requested */
  		|| ((time_status & (STA_PPSTIME|STA_PPSJITTER))
  			== (STA_PPSTIME|STA_PPSJITTER))
  		/* PPS wander exceeded or calibration error when
  		 * PPS frequency synchronization requested
  		 */
  		|| ((time_status & STA_PPSFREQ)
  			&& (time_status & (STA_PPSWANDER|STA_PPSERROR)));
  }
  
  static inline void pps_fill_timex(struct timex *txc)
  {
  	txc->ppsfreq	   = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
  					 PPM_SCALE_INV, NTP_SCALE_SHIFT);
  	txc->jitter	   = pps_jitter;
  	if (!(time_status & STA_NANO))
  		txc->jitter /= NSEC_PER_USEC;
  	txc->shift	   = pps_shift;
  	txc->stabil	   = pps_stabil;
  	txc->jitcnt	   = pps_jitcnt;
  	txc->calcnt	   = pps_calcnt;
  	txc->errcnt	   = pps_errcnt;
  	txc->stbcnt	   = pps_stbcnt;
  }
  
  #else /* !CONFIG_NTP_PPS */
  
  static inline s64 ntp_offset_chunk(s64 offset)
  {
  	return shift_right(offset, SHIFT_PLL + time_constant);
  }
  
  static inline void pps_reset_freq_interval(void) {}
  static inline void pps_clear(void) {}
  static inline void pps_dec_valid(void) {}
  static inline void pps_set_freq(s64 freq) {}
  
  static inline int is_error_status(int status)
  {
  	return status & (STA_UNSYNC|STA_CLOCKERR);
  }
  
  static inline void pps_fill_timex(struct timex *txc)
  {
  	/* PPS is not implemented, so these are zero */
  	txc->ppsfreq	   = 0;
  	txc->jitter	   = 0;
  	txc->shift	   = 0;
  	txc->stabil	   = 0;
  	txc->jitcnt	   = 0;
  	txc->calcnt	   = 0;
  	txc->errcnt	   = 0;
  	txc->stbcnt	   = 0;
  }
  
  #endif /* CONFIG_NTP_PPS */
  
  
  /**
   * ntp_synced - Returns 1 if the NTP status is not UNSYNC
   *
   */
  static inline int ntp_synced(void)
  {
  	return !(time_status & STA_UNSYNC);
  }
  
  
  /*
   * NTP methods:
   */
  
  /*
   * Update (tick_length, tick_length_base, tick_nsec), based
   * on (tick_usec, ntp_tick_adj, time_freq):
   */
  static void ntp_update_frequency(void)
  {
  	u64 second_length;
  	u64 new_base;
  
  	second_length		 = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
  						<< NTP_SCALE_SHIFT;
  
  	second_length		+= ntp_tick_adj;
  	second_length		+= time_freq;
  
  	tick_nsec		 = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
  	new_base		 = div_u64(second_length, NTP_INTERVAL_FREQ);
  
  	/*
  	 * Don't wait for the next second_overflow, apply
  	 * the change to the tick length immediately:
  	 */
  	tick_length		+= new_base - tick_length_base;
  	tick_length_base	 = new_base;
  }
  
  static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
  {
  	time_status &= ~STA_MODE;
  
  	if (secs < MINSEC)
  		return 0;
  
  	if (!(time_status & STA_FLL) && (secs <= MAXSEC))
  		return 0;
  
  	time_status |= STA_MODE;
  
  	return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
  }
  
  static void ntp_update_offset(long offset)
  {
  	s64 freq_adj;
  	s64 offset64;
  	long secs;
  
  	if (!(time_status & STA_PLL))
  		return;
  
  	if (!(time_status & STA_NANO))
  		offset *= NSEC_PER_USEC;
  
  	/*
  	 * Scale the phase adjustment and
  	 * clamp to the operating range.
  	 */
  	offset = min(offset, MAXPHASE);
  	offset = max(offset, -MAXPHASE);
  
  	/*
  	 * Select how the frequency is to be controlled
  	 * and in which mode (PLL or FLL).
  	 */
  	secs = get_seconds() - time_reftime;
  	if (unlikely(time_status & STA_FREQHOLD))
  		secs = 0;
  
  	time_reftime = get_seconds();
  
  	offset64    = offset;
  	freq_adj    = ntp_update_offset_fll(offset64, secs);
  
  	/*
  	 * Clamp update interval to reduce PLL gain with low
  	 * sampling rate (e.g. intermittent network connection)
  	 * to avoid instability.
  	 */
  	if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
  		secs = 1 << (SHIFT_PLL + 1 + time_constant);
  
  	freq_adj    += (offset64 * secs) <<
  			(NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
  
  	freq_adj    = min(freq_adj + time_freq, MAXFREQ_SCALED);
  
  	time_freq   = max(freq_adj, -MAXFREQ_SCALED);
  
  	time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
  }
  
  /**
   * ntp_clear - Clears the NTP state variables
   */
  void ntp_clear(void)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&ntp_lock, flags);
  
  	time_adjust	= 0;		/* stop active adjtime() */
  	time_status	|= STA_UNSYNC;
  	time_maxerror	= NTP_PHASE_LIMIT;
  	time_esterror	= NTP_PHASE_LIMIT;
  
  	ntp_update_frequency();
  
  	tick_length	= tick_length_base;
  	time_offset	= 0;
  
  	/* Clear PPS state variables */
  	pps_clear();
  	spin_unlock_irqrestore(&ntp_lock, flags);
  
  }
  
  
  u64 ntp_tick_length(void)
  {
  	unsigned long flags;
  	s64 ret;
  
  	spin_lock_irqsave(&ntp_lock, flags);
  	ret = tick_length;
  	spin_unlock_irqrestore(&ntp_lock, flags);
  	return ret;
  }
  
  
  /*
   * this routine handles the overflow of the microsecond field
   *
   * The tricky bits of code to handle the accurate clock support
   * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
   * They were originally developed for SUN and DEC kernels.
   * All the kudos should go to Dave for this stuff.
   *
   * Also handles leap second processing, and returns leap offset
   */
  int second_overflow(unsigned long secs)
  {
  	s64 delta;
  	int leap = 0;
  	unsigned long flags;
  
  	spin_lock_irqsave(&ntp_lock, flags);
  
  	/*
  	 * Leap second processing. If in leap-insert state at the end of the
  	 * day, the system clock is set back one second; if in leap-delete
  	 * state, the system clock is set ahead one second.
  	 */
  	switch (time_state) {
  	case TIME_OK:
  		if (time_status & STA_INS)
  			time_state = TIME_INS;
  		else if (time_status & STA_DEL)
  			time_state = TIME_DEL;
  		break;
  	case TIME_INS:
  		if (!(time_status & STA_INS))
  			time_state = TIME_OK;
  		else if (secs % 86400 == 0) {
  			leap = -1;
  			time_state = TIME_OOP;
  			time_tai++;
  			printk(KERN_NOTICE
  				"Clock: inserting leap second 23:59:60 UTC\n");
  		}
  		break;
  	case TIME_DEL:
  		if (!(time_status & STA_DEL))
  			time_state = TIME_OK;
  		else if ((secs + 1) % 86400 == 0) {
  			leap = 1;
  			time_tai--;
  			time_state = TIME_WAIT;
  			printk(KERN_NOTICE
  				"Clock: deleting leap second 23:59:59 UTC\n");
  		}
  		break;
  	case TIME_OOP:
  		time_state = TIME_WAIT;
  		break;
  
  	case TIME_WAIT:
  		if (!(time_status & (STA_INS | STA_DEL)))
  			time_state = TIME_OK;
  		break;
  	}
  
  
  	/* Bump the maxerror field */
  	time_maxerror += MAXFREQ / NSEC_PER_USEC;
  	if (time_maxerror > NTP_PHASE_LIMIT) {
  		time_maxerror = NTP_PHASE_LIMIT;
  		time_status |= STA_UNSYNC;
  	}
  
  	/* Compute the phase adjustment for the next second */
  	tick_length	 = tick_length_base;
  
  	delta		 = ntp_offset_chunk(time_offset);
  	time_offset	-= delta;
  	tick_length	+= delta;
  
  	/* Check PPS signal */
  	pps_dec_valid();
  
  	if (!time_adjust)
  		goto out;
  
  	if (time_adjust > MAX_TICKADJ) {
  		time_adjust -= MAX_TICKADJ;
  		tick_length += MAX_TICKADJ_SCALED;
  		goto out;
  	}
  
  	if (time_adjust < -MAX_TICKADJ) {
  		time_adjust += MAX_TICKADJ;
  		tick_length -= MAX_TICKADJ_SCALED;
  		goto out;
  	}
  
  	tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
  							 << NTP_SCALE_SHIFT;
  	time_adjust = 0;
  
  out:
  	spin_unlock_irqrestore(&ntp_lock, flags);
  
  	return leap;
  }
  
  #ifdef CONFIG_GENERIC_CMOS_UPDATE
  
  static void sync_cmos_clock(struct work_struct *work);
  
  static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
  
  static void sync_cmos_clock(struct work_struct *work)
  {
  	struct timespec now, next;
  	int fail = 1;
  
  	/*
  	 * If we have an externally synchronized Linux clock, then update
  	 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
  	 * called as close as possible to 500 ms before the new second starts.
  	 * This code is run on a timer.  If the clock is set, that timer
  	 * may not expire at the correct time.  Thus, we adjust...
  	 */
  	if (!ntp_synced()) {
  		/*
  		 * Not synced, exit, do not restart a timer (if one is
  		 * running, let it run out).
  		 */
  		return;
  	}
  
  	getnstimeofday(&now);
  	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
  		fail = update_persistent_clock(now);
  
  	next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
  	if (next.tv_nsec <= 0)
  		next.tv_nsec += NSEC_PER_SEC;
  
  	if (!fail)
  		next.tv_sec = 659;
  	else
  		next.tv_sec = 0;
  
  	if (next.tv_nsec >= NSEC_PER_SEC) {
  		next.tv_sec++;
  		next.tv_nsec -= NSEC_PER_SEC;
  	}
  	schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
  }
  
  static void notify_cmos_timer(void)
  {
  	schedule_delayed_work(&sync_cmos_work, 0);
  }
  
  #else
  static inline void notify_cmos_timer(void) { }
  #endif
  
  
  /*
   * Propagate a new txc->status value into the NTP state:
   */
  static inline void process_adj_status(struct timex *txc, struct timespec *ts)
  {
  	if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
  		time_state = TIME_OK;
  		time_status = STA_UNSYNC;
  		/* restart PPS frequency calibration */
  		pps_reset_freq_interval();
  	}
  
  	/*
  	 * If we turn on PLL adjustments then reset the
  	 * reference time to current time.
  	 */
  	if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
  		time_reftime = get_seconds();
  
  	/* only set allowed bits */
  	time_status &= STA_RONLY;
  	time_status |= txc->status & ~STA_RONLY;
  }
  
  /*
   * Called with ntp_lock held, so we can access and modify
   * all the global NTP state:
   */
  static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
  {
  	if (txc->modes & ADJ_STATUS)
  		process_adj_status(txc, ts);
  
  	if (txc->modes & ADJ_NANO)
  		time_status |= STA_NANO;
  
  	if (txc->modes & ADJ_MICRO)
  		time_status &= ~STA_NANO;
  
  	if (txc->modes & ADJ_FREQUENCY) {
  		time_freq = txc->freq * PPM_SCALE;
  		time_freq = min(time_freq, MAXFREQ_SCALED);
  		time_freq = max(time_freq, -MAXFREQ_SCALED);
  		/* update pps_freq */
  		pps_set_freq(time_freq);
  	}
  
  	if (txc->modes & ADJ_MAXERROR)
  		time_maxerror = txc->maxerror;
  
  	if (txc->modes & ADJ_ESTERROR)
  		time_esterror = txc->esterror;
  
  	if (txc->modes & ADJ_TIMECONST) {
  		time_constant = txc->constant;
  		if (!(time_status & STA_NANO))
  			time_constant += 4;
  		time_constant = min(time_constant, (long)MAXTC);
  		time_constant = max(time_constant, 0l);
  	}
  
  	if (txc->modes & ADJ_TAI && txc->constant > 0)
  		time_tai = txc->constant;
  
  	if (txc->modes & ADJ_OFFSET)
  		ntp_update_offset(txc->offset);
  
  	if (txc->modes & ADJ_TICK)
  		tick_usec = txc->tick;
  
  	if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
  		ntp_update_frequency();
  }
  
  /*
   * adjtimex mainly allows reading (and writing, if superuser) of
   * kernel time-keeping variables. used by xntpd.
   */
  int do_adjtimex(struct timex *txc)
  {
  	struct timespec ts;
  	int result;
  
  	/* Validate the data before disabling interrupts */
  	if (txc->modes & ADJ_ADJTIME) {
  		/* singleshot must not be used with any other mode bits */
  		if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
  			return -EINVAL;
  		if (!(txc->modes & ADJ_OFFSET_READONLY) &&
  		    !capable(CAP_SYS_TIME))
  			return -EPERM;
  	} else {
  		/* In order to modify anything, you gotta be super-user! */
  		 if (txc->modes && !capable(CAP_SYS_TIME))
  			return -EPERM;
  
  		/*
  		 * if the quartz is off by more than 10% then
  		 * something is VERY wrong!
  		 */
  		if (txc->modes & ADJ_TICK &&
  		    (txc->tick <  900000/USER_HZ ||
  		     txc->tick > 1100000/USER_HZ))
  			return -EINVAL;
  	}
  
  	if (txc->modes & ADJ_SETOFFSET) {
  		struct timespec delta;
  		delta.tv_sec  = txc->time.tv_sec;
  		delta.tv_nsec = txc->time.tv_usec;
  		if (!capable(CAP_SYS_TIME))
  			return -EPERM;
  		if (!(txc->modes & ADJ_NANO))
  			delta.tv_nsec *= 1000;
  		result = timekeeping_inject_offset(&delta);
  		if (result)
  			return result;
  	}
  
  	getnstimeofday(&ts);
  
  	spin_lock_irq(&ntp_lock);
  
  	if (txc->modes & ADJ_ADJTIME) {
  		long save_adjust = time_adjust;
  
  		if (!(txc->modes & ADJ_OFFSET_READONLY)) {
  			/* adjtime() is independent from ntp_adjtime() */
  			time_adjust = txc->offset;
  			ntp_update_frequency();
  		}
  		txc->offset = save_adjust;
  	} else {
  
  		/* If there are input parameters, then process them: */
  		if (txc->modes)
  			process_adjtimex_modes(txc, &ts);
  
  		txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
  				  NTP_SCALE_SHIFT);
  		if (!(time_status & STA_NANO))
  			txc->offset /= NSEC_PER_USEC;
  	}
  
  	result = time_state;	/* mostly `TIME_OK' */
  	/* check for errors */
  	if (is_error_status(time_status))
  		result = TIME_ERROR;
  
  	txc->freq	   = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
  					 PPM_SCALE_INV, NTP_SCALE_SHIFT);
  	txc->maxerror	   = time_maxerror;
  	txc->esterror	   = time_esterror;
  	txc->status	   = time_status;
  	txc->constant	   = time_constant;
  	txc->precision	   = 1;
  	txc->tolerance	   = MAXFREQ_SCALED / PPM_SCALE;
  	txc->tick	   = tick_usec;
  	txc->tai	   = time_tai;
  
  	/* fill PPS status fields */
  	pps_fill_timex(txc);
  
  	spin_unlock_irq(&ntp_lock);
  
  	txc->time.tv_sec = ts.tv_sec;
  	txc->time.tv_usec = ts.tv_nsec;
  	if (!(time_status & STA_NANO))
  		txc->time.tv_usec /= NSEC_PER_USEC;
  
  	notify_cmos_timer();
  
  	return result;
  }
  
  #ifdef	CONFIG_NTP_PPS
  
  /* actually struct pps_normtime is good old struct timespec, but it is
   * semantically different (and it is the reason why it was invented):
   * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
   * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
  struct pps_normtime {
  	__kernel_time_t	sec;	/* seconds */
  	long		nsec;	/* nanoseconds */
  };
  
  /* normalize the timestamp so that nsec is in the
     ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
  static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
  {
  	struct pps_normtime norm = {
  		.sec = ts.tv_sec,
  		.nsec = ts.tv_nsec
  	};
  
  	if (norm.nsec > (NSEC_PER_SEC >> 1)) {
  		norm.nsec -= NSEC_PER_SEC;
  		norm.sec++;
  	}
  
  	return norm;
  }
  
  /* get current phase correction and jitter */
  static inline long pps_phase_filter_get(long *jitter)
  {
  	*jitter = pps_tf[0] - pps_tf[1];
  	if (*jitter < 0)
  		*jitter = -*jitter;
  
  	/* TODO: test various filters */
  	return pps_tf[0];
  }
  
  /* add the sample to the phase filter */
  static inline void pps_phase_filter_add(long err)
  {
  	pps_tf[2] = pps_tf[1];
  	pps_tf[1] = pps_tf[0];
  	pps_tf[0] = err;
  }
  
  /* decrease frequency calibration interval length.
   * It is halved after four consecutive unstable intervals.
   */
  static inline void pps_dec_freq_interval(void)
  {
  	if (--pps_intcnt <= -PPS_INTCOUNT) {
  		pps_intcnt = -PPS_INTCOUNT;
  		if (pps_shift > PPS_INTMIN) {
  			pps_shift--;
  			pps_intcnt = 0;
  		}
  	}
  }
  
  /* increase frequency calibration interval length.
   * It is doubled after four consecutive stable intervals.
   */
  static inline void pps_inc_freq_interval(void)
  {
  	if (++pps_intcnt >= PPS_INTCOUNT) {
  		pps_intcnt = PPS_INTCOUNT;
  		if (pps_shift < PPS_INTMAX) {
  			pps_shift++;
  			pps_intcnt = 0;
  		}
  	}
  }
  
  /* update clock frequency based on MONOTONIC_RAW clock PPS signal
   * timestamps
   *
   * At the end of the calibration interval the difference between the
   * first and last MONOTONIC_RAW clock timestamps divided by the length
   * of the interval becomes the frequency update. If the interval was
   * too long, the data are discarded.
   * Returns the difference between old and new frequency values.
   */
  static long hardpps_update_freq(struct pps_normtime freq_norm)
  {
  	long delta, delta_mod;
  	s64 ftemp;
  
  	/* check if the frequency interval was too long */
  	if (freq_norm.sec > (2 << pps_shift)) {
  		time_status |= STA_PPSERROR;
  		pps_errcnt++;
  		pps_dec_freq_interval();
  		pr_err("hardpps: PPSERROR: interval too long - %ld s\n",
  				freq_norm.sec);
  		return 0;
  	}
  
  	/* here the raw frequency offset and wander (stability) is
  	 * calculated. If the wander is less than the wander threshold
  	 * the interval is increased; otherwise it is decreased.
  	 */
  	ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
  			freq_norm.sec);
  	delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
  	pps_freq = ftemp;
  	if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
  		pr_warning("hardpps: PPSWANDER: change=%ld\n", delta);
  		time_status |= STA_PPSWANDER;
  		pps_stbcnt++;
  		pps_dec_freq_interval();
  	} else {	/* good sample */
  		pps_inc_freq_interval();
  	}
  
  	/* the stability metric is calculated as the average of recent
  	 * frequency changes, but is used only for performance
  	 * monitoring
  	 */
  	delta_mod = delta;
  	if (delta_mod < 0)
  		delta_mod = -delta_mod;
  	pps_stabil += (div_s64(((s64)delta_mod) <<
  				(NTP_SCALE_SHIFT - SHIFT_USEC),
  				NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
  
  	/* if enabled, the system clock frequency is updated */
  	if ((time_status & STA_PPSFREQ) != 0 &&
  	    (time_status & STA_FREQHOLD) == 0) {
  		time_freq = pps_freq;
  		ntp_update_frequency();
  	}
  
  	return delta;
  }
  
  /* correct REALTIME clock phase error against PPS signal */
  static void hardpps_update_phase(long error)
  {
  	long correction = -error;
  	long jitter;
  
  	/* add the sample to the median filter */
  	pps_phase_filter_add(correction);
  	correction = pps_phase_filter_get(&jitter);
  
  	/* Nominal jitter is due to PPS signal noise. If it exceeds the
  	 * threshold, the sample is discarded; otherwise, if so enabled,
  	 * the time offset is updated.
  	 */
  	if (jitter > (pps_jitter << PPS_POPCORN)) {
  		pr_warning("hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
  		       jitter, (pps_jitter << PPS_POPCORN));
  		time_status |= STA_PPSJITTER;
  		pps_jitcnt++;
  	} else if (time_status & STA_PPSTIME) {
  		/* correct the time using the phase offset */
  		time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
  				NTP_INTERVAL_FREQ);
  		/* cancel running adjtime() */
  		time_adjust = 0;
  	}
  	/* update jitter */
  	pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
  }
  
  /*
   * hardpps() - discipline CPU clock oscillator to external PPS signal
   *
   * This routine is called at each PPS signal arrival in order to
   * discipline the CPU clock oscillator to the PPS signal. It takes two
   * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
   * is used to correct clock phase error and the latter is used to
   * correct the frequency.
   *
   * This code is based on David Mills's reference nanokernel
   * implementation. It was mostly rewritten but keeps the same idea.
   */
  void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
  {
  	struct pps_normtime pts_norm, freq_norm;
  	unsigned long flags;
  
  	pts_norm = pps_normalize_ts(*phase_ts);
  
  	spin_lock_irqsave(&ntp_lock, flags);
  
  	/* clear the error bits, they will be set again if needed */
  	time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
  
  	/* indicate signal presence */
  	time_status |= STA_PPSSIGNAL;
  	pps_valid = PPS_VALID;
  
  	/* when called for the first time,
  	 * just start the frequency interval */
  	if (unlikely(pps_fbase.tv_sec == 0)) {
  		pps_fbase = *raw_ts;
  		spin_unlock_irqrestore(&ntp_lock, flags);
  		return;
  	}
  
  	/* ok, now we have a base for frequency calculation */
  	freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
  
  	/* check that the signal is in the range
  	 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
  	if ((freq_norm.sec == 0) ||
  			(freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
  			(freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
  		time_status |= STA_PPSJITTER;
  		/* restart the frequency calibration interval */
  		pps_fbase = *raw_ts;
  		spin_unlock_irqrestore(&ntp_lock, flags);
  		pr_err("hardpps: PPSJITTER: bad pulse\n");
  		return;
  	}
  
  	/* signal is ok */
  
  	/* check if the current frequency interval is finished */
  	if (freq_norm.sec >= (1 << pps_shift)) {
  		pps_calcnt++;
  		/* restart the frequency calibration interval */
  		pps_fbase = *raw_ts;
  		hardpps_update_freq(freq_norm);
  	}
  
  	hardpps_update_phase(pts_norm.nsec);
  
  	spin_unlock_irqrestore(&ntp_lock, flags);
  }
  EXPORT_SYMBOL(hardpps);
  
  #endif	/* CONFIG_NTP_PPS */
  
  static int __init ntp_tick_adj_setup(char *str)
  {
  	ntp_tick_adj = simple_strtol(str, NULL, 0);
  	ntp_tick_adj <<= NTP_SCALE_SHIFT;
  
  	return 1;
  }
  
  __setup("ntp_tick_adj=", ntp_tick_adj_setup);
  
  void __init ntp_init(void)
  {
  	ntp_clear();
  }
  